Propulsion systems powered by internal combustion engines are commonly used on boats and other watercraft. Typically, these systems have been designed for use either in deep water conditions or shallow water conditions, but not both. Most often, such propulsion systems are not adapted for conditions in which floating debris is suspended in the surrounding water. Regardless of the type of use which is intended, many of these systems employ a power source which is connected to a drive shaft which, in turn, is connected to a propeller in physical contact with the water. Variations of this typical configuration include, for example, systems which employ forced water (i.e., water jet propulsion) or forced air (i.e., air propulsion) without the use of a propeller in physical contact with the water. As one might expect, different advantages are presented by the various system configurations. A principal means of assessing a particular propulsion system is its versatility in varying water conditions. For example, deep, clean bodies of water present different operating conditions for a propulsion system as compared to bodies of water which are partially or substantially shallow, or bodies of water in which vegetation or other debris may be suspended. Systems which employ a fixed propeller which cannot be removed from the water during operation are not compatible with use in shallow waters, since the probabilities of watercraft grounding and/or damage to the propeller are greater. Those which employ water jet propulsion are also vulnerable under such conditions or in conditions where vegetation or other debris is suspended in the water, since these systems typically require a water intake port which can become clogged in such circumstances, thereby causing the system to fail. Even air boats or other craft which are propelled by large rotating fans powered by internal combustion engines present disadvantages for the user because of, for example, increased noise, excessive size (as it affects space available on the watercraft), increased danger (due to the large rotating blades), and significant limitations on reversing the direction of propulsion. Moreover, such air boat configurations typically are not stable enough for proper functioning in deep water conditions.
Regardless of the propulsion system, the internal combustion engine component generates significant heat during operation, and such heat in large part must be transferred away for the engine to perform properly. In marine applications, including both fresh, salt and brackish water conditions, such engines commonly are engineered to include a cooling system which circulates water from outside the watercraft through the engine block to transfer heat away from the engine. Such cooling systems are often referred to as open cooling systems, since these systems permit the inflow of a heat-conductive fluid from an external source, and the outflow of the heated fluid from the system without any recirculation. This is contrasted with closed cooling systems which recirculate a heat-conductive fluid through the engine into an accompanying radiator or other apparatus which transfers heat from the fluid to the surrounding air. Open cooling systems have been preferred in marine applications because of limitations posed by closed cooling systems that require a significant influx of air for heat transfer purposes. Such systems are typically avoided in marine applications in favor of the open cooling systems because of the requirement in closed systems of loud cooling fans or the like to provide air for cooling.
However, a major disadvantage of open cooling systems in internal combustion engines for marine applications is highlighted when the water being traversed is shallow and/or filled with vegetation or other floating debris. Under such circumstances, the inflow of fresh water to the open cooling system or the outflow of heated water from the open cooling system can be significantly impaired when mud, silt, sand, or other debris clogs the system's water flow path. Engine overheating is often the result because the cooling system becomes inoperative as the flow of fresh water through the system is impaired. Additionally, when the water being traversed is salt water or brackish water, corrosion of the various component parts of the cooling system becomes a legitimate concern.
Hence, a need exists for a universal watercraft propulsion system employing an internal combustion engine which enjoys the advantages of open cooling systems in internal combustion engines for marine applications in deep water conditions, while avoiding the disadvantages of such open cooling systems when applied in waters which are shallow and/or filled with vegetation or other floating debris.
In addition, notwithstanding recent advances in reversible pitch propeller technology, propulsion systems employing reversible pitch propellers heretofore have failed to effectively control water flow around the propeller in both forward and reverse pitch settings, especially during application of moderate to high system throttle. Thus, a need also exists for a universal propulsion system which employs, in a highly effective manner, weedless and reversible pitch propeller technology. This need is especially evident in shallow waters, where effective reversive thrust is imperative for maneuvering watercraft around and over sand bars, tree stumps, thick patches of floating vegetation, and the like.